For some limnological and oceanographic studies it is important that samples of water at different depths be taken and that such samples be protected against dilution or modification due to leakage of the sampler during retrieval of the latter. The Kemmerer style water sampler was designed for this purpose and comprises a hollow tube, normally open at both ends, and having top and bottom closures or stoppers which are adapted to be moved from open positions to sealing positions in response to the dropping of a weighted messenger along the line or cable which supports the sampler. The stoppers of a Kemmerer style sampler are latched in their open positions and the upper stopper includes a latch release mechanism which is tripped by the weighted messenger to enable the stoppers to move to their closed positions. Such samplers, however, have their limitations, particularly when the sampler is to be used in a position where it and the line are inclined to the vertical because of currents or the like, as a result of which the weighted messenger may be unable to descend to the sampler or may be unable to strike the release mechanism with a force insufficient to trip the latch.